Operation of an internal combustion engine generally includes adjusting the fuel injectors and engine spark. In addition, operation of an internal combustion engine generally includes adjusting a throttle to control the amount of air that flows through an intake manifold to an intake port of the internal combustion engine. During a shutdown of the internal combustion engine, the fuel injectors are adjusted so that fuel injection is discontinued and engine spark is halted. However, control of the amount of air that flows through the intake manifold to the intake port of the combustion chamber can be limited to an open loop control of the throttle to a default position that provides an intake manifold that is significantly open.
At low operating speeds of an internal combustion engine that corresponds to a shutdown, a significantly open intake manifold allows the manifold pressure to increase and also allows a greater charge of air into the cylinders of the engine. As can be appreciated by one of ordinary skill in the art, an increase in the manifold pressure and a greater charge of air into the cylinders of the engine causes the engine cylinders to compress full charges of air, and increased torque pulses are exerted on the engine block. Minimal pumping work is typically necessary to bring in the air charge. Therefore, the engine shutdown event is extended due to the lack of throttling losses, and a significant back and forth roll can exist during engine shutdown at a frequency corresponding to the engine firing frequency. This back and forth roll at a frequency corresponding to the engine firing order, which is generally know as engine shudder, is undesirable.
In view of the foregoing, it should be appreciated that it would be desirable to provide methods and apparatus for controlling a vehicle engine such that engine shudder is minimized during a shutdown of the vehicle engine. Furthermore, additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and following detailed description of a preferred exemplary embodiment and appended claims.